Color Flow Doppler required engineering advances in signal processing. A major issue was simply separating the imaging signal from the Doppler signal.

Engineers at Hewlett-Packard, Paul Magnin in particular, thought it was fairly obvious that physicians would like to measure and display velocity at every point in the image. They just did not know how to achieve it. After struggling to get the Doppler unit out, Magnin started to investigate color flow, developing some computer algorithms to process the signal. At the same time a paper published by the American Institute of Ultrasound Medicine from Aloka Research Labs showed an actual picture of a mechanically swept color flow image. Clearly it could be done, and done commercially. Consequently, development efforts were stepped up and from eight different algorithms, two were selected that seemed most likely to answer the call. It was not entirely clear which one would be more appropriate, so simulations were set up to test one algorithm against the other. Once clinicians saw the video of the various algorithms, however, it was not clear that color flow would be of clinical significance. Nonetheless, Hewlett-Packard pushed ahead with its development because it believed the technology has potential.

The path from concept to prototype was arduous. It seemed that color flow would require a redesign of the system architecture, which had not been designed to be upgradable. Once a redesign was begun it was nearly impossible to prevent everyone's pet projects from being added to the revision. Introduction of the product seemed to be far away. Another engineer, again working off the critical path, found a solution to move the product into the marketplace more quickly—sell it as an upgrade. Although this solution was very well received, the decision to offer Color Flow Doppler as an upgrade postponed some of the redesign problems to the next revision.

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